


The Potential Fatality of Assuming

by crossroadswrite



Category: Teen Wolf (TV)
Genre: Alternate Universe - Everyone Lives/Nobody Dies, Babysitter Derek Hale, Fluff, Future Fic, Getting Together, Kid Fic, M/M, Misunderstandings, Pining Stiles Stilinski, kinda v lowkey if u consider stiles jumping to conclusions a misunderstanding
Language: English
Status: Completed
Published: 2016-09-13
Updated: 2016-09-13
Packaged: 2018-08-14 20:36:39
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,196
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8028088
Author URL: https://archiveofourown.org/users/crossroadswrite/pseuds/crossroadswrite
Summary: The hair, the buttons and the general happy and slightly tired disposition with which Derek came back from his secret exploits were as obvious as a glaring neon sign flashing the words JUST GOT LAID.
A sign that Stiles ignored because he had a seven year plan god damn it.
(OR: in which Stiles assumes things, gets accosted by the sister he never/always wanted, discovers he was horribly wrong, almost dies via Derek Hale with kids, can't handle all that collarbone action, uses tickling as the ultimate mode of revenge, and gets a boyfriend. In that order.)





	The Potential Fatality of Assuming

**Author's Note:**

> so many thanks to the light of my life, my bro [LadyDrace](http://archiveofourown.org/users/LadyDrace/works) for beta-ing this fic for me. check minna out y'all she's a+++ at the writing thing.
> 
> list of things i google searched for this fic:  
> -baby spit up images  
> -jizz stains images  
> -name of the teenage mutant ninja turtles  
> -name of that strappy chest basket for babies

Stiles discovers Derek has a boyfriend on a Friday night.

Friday nights are pack nights and the only day of the week Stiles has an excuse to sprawl on Derek’s couch, drink all his healthy disgusting yogurt and pretend not to give him heart eyes.

Friday nights are sacred for Stiles, mostly because he gets to watch Derek in his natural habitat, softly growling at Erica when she steals his spot in his armchair, passive aggressively making sure everyone is well fed, diplomatically being the deciding vote in which movie they’re going to watch, firmly talking them out of stupid plans when they’re piss drunk on laced liquor.

Fridays are the only days where Stiles can indulge in shamelessly staring at Derek and trading light banter with him without the threat of something big and dangerous lurking over their heads.

Fridays are when Stiles takes mental notes about all the little endearing things Derek does, his likes and dislikes, what he twists his nose at and what makes that secret little smile tilt his lips. Fridays are primetime for collecting data to work into his seven year plan to marry Derek and be settled down with a job and a dog.

It’s because he watches Derek so much that he starts noticing little things that just seem… off.

First it’s his hair.

Stiles is well acquainted with the many styled looks of Derek’s hair, from the traditional bro spiky hair to that glorious summer after high school where Derek had gone full mountain man and let his hair and beard grow out. Stiles had dubbed it prince hair and spent the summer restraining himself from touching it.

Being well acquainted with how Derek normally keeps his hair, and how often he grooms himself, Stiles immediately notices the messy hair, sticking up every which way like someone has been clutching and tugging at it.

At first, Stiles had just thought maybe Derek had a stressful day and fell into the habit of tugging it or maybe he just didn’t bother gelling it that morning, but then he quickly realized that couldn’t be it when it Derek’s hair turned from gelled in the mornings to an absolute wreck in the afternoons.

Then it was the buttons of his Henleys, how every once in a while the top one would be ripped off, how the neckline would be stretched loose around Derek’s collarbones.

That’s when Stiles started to get suspicious. When the pieces of the puzzle slowly started adding up.

The hair, the buttons and the general happy and slightly tired disposition with which Derek came back from his secret exploits were as obvious as a glaring neon sign flashing the words JUST GOT LAID.

A sign that Stiles ignored because he had a seven year plan god damn it.

A sign he can’t ignore when Derek waltzes in for pack night, _late_ , cheeks slightly flushed, shoulders relaxed, his hair a mess, the button on his shirt ripped off and a suspicious stain on his shirt.

It’s the stain that gets him, coupled with the knowledge that Derek never stains his shirts, no matter how messy what he’s eating is. The stain is too high on his shoulder to be food anyway, and Stiles has to close his eyes against the image of Derek on his knees for someone.

That is the fateful day Stiles has to acknowledge the fact that Derek has a secret boyfriend he’s been keeping from the pack, that Derek has been going out and getting laid, that all those lingering glances and touches between them were all in his head and Derek never had any interest in Stiles to start with.

He sinks into the couch cushions dejectedly, jealousy and defeat swirling nastily in the pit of his stomach, and making him slightly sick.

“Why do you smell sad?” Erica asks, subtle as a tractor causing a traffic jam.

“I don’t.”

She twists her nose. “You do, and it’s disgusting. So stop it,” she demands and then flops down on top of him and wrestles his head under her arm to give him a noogie.

“Erica, stop bullying Stiles.”

“It’s not bullying! It’s sibling love!” Erica shouts and laughs at Stiles’ batting hands.

Stiles huffs a laugh and keeps trying to push her off halfheartedly, until her weight suddenly disappears.

He looks up to see Derek physically picking Erica up and plopping her on Boyd’s lap before he sits next to Stiles and offers him a bag of red vines.

“I saved some for you before Scott had time to raid the kitchen,” he says, all tentative and shy and Stiles’ life is just _not fair_.

He sighs, and takes the bag from Derek.

“Thanks.”

It’s utterly ridiculous how all it takes is one shy smile from Derek for hope to swell in Stiles’ heart and make him think, maybe, _maybe_ if I just wait this out…

«»

Derek doesn’t have a boyfriend and Stiles might have made a slight miscalculation that could very well cost him his life.

“Hey, didn’t expect to see you here,” says Derek Hale, casually, walking towards Stiles with a tiny little squirming baby securely tucked into a baby carrier strapped to his chest and a giggling toddler on his shoulders.

Stiles chokes on his own spit, eyes wide and heart a melted puddle of goo on the floor.

“Who this?” the kid on Derek’s shoulder asks, tugging on Derek’s hair to catch his attention.

“This is my friend Stiles.”

The kid gasps. “Pretty Stiles, that plays with the wolves? Like in the stories?”

Derek goes red in the ears and coughs awkwardly, looking away.

“You think I’m pretty?” Stiles blurts out.

“I mean-“

“Yeah! Because you’re a prince, right? And all princes are pretty! Derek says so! He also says everyone can be princes! And that princes are always nice and save people and you save Derek a bunch, right? So you’re a pretty prince!”

“I… save him…”

“In the stories at nap time. Derek is the _best_ at naptime stories. He knows a _ton_ and he does all the voices,” the kid says smugly, tugging on Derek’s hair in their excitement.

Derek’s flush slowly spreads down his cheeks and into the dip of his neckline, and Stiles can’t help but follow it, wonder just how low it goes, which turns out to be a terrible idea, because the baby cradled against Derek’s chest has grabbed a hold of his neckline with one stubborn little fist and is tugging it down insistently, trying to get the fabric in their mouth as it kicks its legs energetically, giving Stiles a peek of how low the flush goes as well as Derek’s glorious chest hair.

Stiles kind of wants to pet it, but then again he always kind of wants to pet Derek’s scruff and hair and just luxuriate in the feeling of closeness that he’s not allowed to have.

“Nice kids,” Stiles says, desperately trying to focus on anything that won’t cause him a boner in the middle of a grocery store.

“Thanks,” Derek says awkwardly. “One of my old high school friends needed a babysitter and I don’t really have anything else to do.” He shrugs, jostling the kid on his shoulders and making them giggle.

“It’s nice,” Stiles says. “You look nice, with kids, I mean.” He scratches the back of his neck awkwardly.

This whole exchange has left him feeling off-balance, hopeful, and like he should shorten his seven year plan to a four year plan because the image Derek makes, standing in a grocery store with kids hanging off of him, is something that Stiles wants so badly he aches with it.

Rationally, he knows it’s something ridiculous to want. _Rationally_ , he knows he shouldn’t be thinking about names and who the godparents would be or what color to paint the nursery or how the new Hale house has the advantage of having a great school district close by.

“Is Stiles coming to play with us, Uncle Dee? We could have a tea party,” the kid gasps, “or play teenage mutant ninja turtles! He can be Donatello.”

“I’m not sure-“

“Sure!” Stiles says brightly. “It’s my day off, so it’s not like I have anything to do. I mean, if you don’t mind, of course.”

“I don’t mind, if you don’t mind.”

“Well, I don’t mind.”

“Good.”

“Awesome.”

“Adults are weird,” the kid says and kicks Derek in the bicep with their heel.

«»

They end up going to the local park and having a mini mid-afternoon picnic.

Jamie runs around them yelling and dramatically flopping on Stiles to demand to be handfed cookies just for an excuse to try to bite Stiles’ fingers before giggling and running off again, while Derek sits patiently with tiny Ollie on his lap, the baby kicking their little arms and feet about like they're trying really hard to say _fuck you_ to the laws of gravity and swim around in the air, or, possibly, singlehandedly start a rave party with their sweet dance moves, and Stiles-

Stiles looks at Derek and tries not to be distracted by his messy hair and flushed cheeks and general soft and happy demeanor.

“You’re staring,” Derek says quietly, in-between making airplane noises and trying to get Ollie to eat his yogurt from a colorful spoon.

“You don’t have a boyfriend,” Stiles says, because his foot missed his mouth and wanted to shove itself in it once more.

“What?”

“What.”

“You thought I had a boyfriend?”

“I might’ve been… under the _slight_ impression that you had _someone_.”

Derek furrows his brows, his nose twitches in distaste at the concept of dating.

“Who would even-“

“Who _wouldn’t_ ,” says Stiles, too quickly, cutting the thought before it has a chance to voice itself.

Derek looks at him intensely, eyes boring into Stiles’ in that way he has when he’s trying to figure Stiles out. The moment feels charged; it feels like they’re on a cliff’s edge, so close to falling, so easily-

And then Ollie whacks their spoon and a glob of yogurt smacks Derek in the cheek. Jamie stops running to laugh, rolls over into the soft grass and starts kicking their arms and legs.

“I’m a turtle,” they say, and Stiles takes his chance to exact his revenge through the horror that is tickling.

It lasts until Jamie rolls away and hides behind Derek, the best position to still get cookies and make faces at Stiles.

Derek is still looking at him, though. Eyes soft in the corners and mouth upturned the slightest bit.

“I don’t have a boyfriend,” Derek says, calm as you please. “Do you?”

Stiles rolls his eyes. As if there would be anyone else. “No.”

Derek is quiet for half a second, bouncing Ollie distractedly on his knee, and then, “would you like one?”

Stiles’ mouth drops open. “Are you offering?” he chokes out.

“Yes,” Derek says, easy as that.

Stiles can feel the flush heating up high on his cheekbones, and at least he matches the red in Derek’s ears.

“Okay,” he says, heart hammering in his chest, wiping off his sweaty palms on his jeans.

“Good,” Derek says, ducking his chin and looking pleased as punch.

Ollie grabs a hold of his shirt and starts pulling, attempting to get up on their feet and reach Derek’s nose so they can shove their tiny little fingers up it.

Stiles has to swallow and look away for a bit.

“Awesome.”

“Does this mean you’re married now?” Jamie asks smartly, leaning so far over Derek’s shoulder they’re hanging off of it.

“Not yet,” Stiles says.

Derek chokes on nothing and Stiles grins.

“For that, I have a three year plan.”

Jamie scrunches their whole face at him. “Lame. Can we go on the swings now?”

«»

The pack finds out Derek has a boyfriend on a Friday night, when they’re all gathered around the room watching Mulan and eating their combined weight in pizza.

There are little clues that they pick up, like how Derek is mellow and agreeable, humming, and how Derek has a red mark shaped like a hickey peeking through the stretched collar of his Henley, and how both sides of his bed are messed up now, and how he keeps saying he has _plans_ with someone, and how he grabs Stiles by the waist, brings him down to his lap and spends the entire time nuzzling softly into his neck and snorting at Stiles’ lame running commentary.

Overall they take it pretty well, if you consider Isaac punching Jackson in the stomach with a huge smile and asking for _his money, bitches, oh yeah I’m going to buy all the poptarts_.

Stiles is too busy openly staring at Derek and reveling in the fact that he gets this, so easily, without the need of convoluted plans or humiliation; he gets this because Derek _likes_ him, stares at Stiles adoringly as much as Stiles stares at Derek.

Friday nights are still sacred for Stiles, especially because when the night ends and everyone leaves the loft, he gets to stay for as long as he likes.

He ends up staying forever.

**Author's Note:**

> *leans real close and whispers* derek hale is a smooth af goober pass it on


End file.
